In general, a LSI that is a semiconductor integrated circuit handling image data in a digital camera and the like is mounted with an image processing circuit that is a data processing circuit performing image processing of input image data. As described in Unexamined Japanese Patent Application Kokai Publication No. H7-30374, for example, a most part of this image processing circuit comprises an arithmetic unit such as an adder, a multiplier, a divider, and the like.
However, this image processing is not always performed. In some cases, an image of input image data is not processed and then output as-is.
For example, when an image processing circuit is a moving image filter circuit, it is required not to use a moving image filter for still image shooting. In this case, a filter coefficient of a targeted pixel is set to be 1 and filter coefficients other than the targeted pixel are set to be 0, resulting in that a filter function becomes OFF to output input data as-is.
FIG. 1 is a block diagram illustrating one example of a conventional filter circuit.
In FIG. 1, the symbol 10 represents a horizontal filter in a semiconductor integrated circuit.
Herein, the horizontal filter 10 comprises registers 101 to 105, multipliers 111 to 115, and adders 121 to 124.
Now, a filter function of this horizontal filter 10 is allowed to be OFF and then input pixel data T0 is output as-is. Data of targeted pixel is designated as T8; and then a filter coefficient T3 of the multiplier 113 for multiplying the data of targeted pixel T8 by the coefficient is set to be 1, and filter coefficients T1, T2, T4, and T5 of those other than the multiplier 113 are set to be 0. This coefficient setting causes output data T13 of the multiplier 113 to have the same value as the data of targeted pixel T8. In addition, output data T11, T12, T14, and T15 of the multipliers 111, 112, 114, and 115 have a value of 0, respectively. Therefore, a value of output data, a filter output, T19 of the adder 124 at a final stage becomes the same value as the data of targeted pixel T8. In other words, the filter function of the horizontal filter 10 becomes OFF and then input data is output as-is without undergoing filtering.
However, in the horizontal filter 10, even when input data processing is unnecessary, the multipliers and the adders configuring the horizontal filer 10 still operate, resulting in a large amount of power consumption.
In this manner, a semiconductor integrated circuit provided with a conventional data processing circuit has produced a problem that even when data processing using a data processing circuit is unnecessary, arithmetic units configuring the data processing circuit still operate, resulting in power consumption.